Effects of different solvent baths on the performances of dye-sensitized solar cells: Experimental and theoretical investigation

ORGELE 2633

No. of Pages 10, Model 3G

4 July 2014 Organic Electronics xxx (2014) xxx–xxx 1

Contents lists available at ScienceDirect

Organic Electronics journal homepage: www.elsevier.com/locate/orgel 6 7

Effects of different solvent baths on the performances of dye-sensitized solar cells: Experimental and theoretical investigation

3 4 5 8 9 10 11 12 14 13 15 1 3 7 0 18 19 20 21 22 23 24 25 26 27 28 29

Q1

Ximing Chen a, Chunyang Jia a,⇑, Zhongquan Wan a, Juan Feng b, Xiaojun Yao c a State Key Laboratory of Electronic Thin Films and Integrated Devices, School of Microelectronics and Solid-State Electronics, University of Electronic Science and Technology of China, Chengdu 610054, PR China b School of Life Science and Technology, University of Electronic Science and Technology of China, Chengdu 610054, PR China c State Key Laboratory of Applied Organic Chemistry, School of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, PR China

a r t i c l e

i n f o

Article history: Received 27 February 2014 Received in revised form 30 May 2014 Accepted 20 June 2014 Available online xxxx Keywords: Solvent effects TiO2 cluster Density functional theory (DFT) Photovoltaic performance Dye-sensitized solar cells (DSSCs)

a b s t r a c t Combining experimental analyses and computational modeling, we investigated CD-7-sensitized solar cells (DSSCs) by THF or DMF bath with aim to understand the effects of different solvent baths on the performances of the corresponding DSSCs. In experiment, the photophysical, photovoltaic and electrochemical impedance properties of the DSSCs based on THF or DMF bath were investigated. The UV–vis spectrum of CD-7 in THF is red-shifted in comparison with it in DMF, indicating that there is a different interaction between CD-7 and the solvent molecules. The UV–vis spectrum of CD-7 adsorbed on TiO2 film suggested that different solvent baths have a different effect on the J-aggregation and absorption strength. Monochromatic incident photon-to-electron conversion efficiency (IPCE) and electrochemical impedance analyses showed that different solvent baths have a significant influence on the IPCE values and electron lifetimes of the corresponding DSSCs. The analysis results of computational modeling showed that the solvent molecules would affect the energy level of TiO2, adsorption structure and adsorbed amount of CD-7 on the TiO2 film. The above analysis results illuminate a big difference in the performances of DSSCs by THF or DMF bath. The DSSCs based on THF bath obtained the g value 1.53%, which is about twice as much as that of DMF bath. Ó 2014 Published by Elsevier B.V.

31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49

50 51

1. Introduction

52

Dye-sensitized solar cells (DSSCs), developed by Grätzel and coworkers, have attracted considerable attention of many research groups in the past two decades owing to their high efficiencies and low costs [1]. DSSCs typically contain four components: a mesoporous semiconductor metal oxide film, a dye, an electrolyte/hole transporter, and a counter electrode [2]. Various attempts toward the modification of these different components have been

53 54 55 56 57 58 59

⇑ Corresponding author. Tel.: +86 28 83201991; fax: +86 28 83202569. E-mail address: [email protected] (C. Jia).

carried out to improve the overall conversion efficiency of DSSCs. In particular, extensive studies on the development of highly efficient dyes have been carried out as they play a crucial role on the performances of DSSCs. Up to now, DSSCs based on ruthenium dyes and porphyrin dyes have shown very impressive solar to electric power conversion efficiencies. The DSSC based on black dye with donor–acceptor type coadsorbent has reached an overall solar energy conversion efficiency (g) of 11.4% [3], and porphyrin-sensitized solar cell with cobalt (II/III)-based redox electrolyte has obtained a new record efficiency of 13% [4]. On the other hand, the preparation of the dye-sensitized TiO2 photoelectrode is also important for the higher

http://dx.doi.org/10.1016/j.orgel.2014.06.026 1566-1199/Ó 2014 Published by Elsevier B.V.

Please cite this article in press as: X. Chen et al., Effects of different solvent baths on the performances of dye-sensitized solar cells: Experimental and theoretical investigation, Org. Electron. (2014), http://dx.doi.org/10.1016/j.orgel.2014.06.026

60 61 62 63 64 65 66 67 68 69 70 71 72

ORGELE 2633

No. of Pages 10, Model 3G

4 July 2014 2

X. Chen et al. / Organic Electronics xxx (2014) xxx–xxx

NC COOH

N N H

Fig. 1. Chemical structure of dye CD-7.

108

performances of DSSCs because many photo- and electrochemical reactions, such as photoexcitation of dyes, the electron injection from dyes to TiO2, and the reduction of the oxidized form of dyes occur at the dye/TiO2 interface. In the processes of preparing dye-sensitized TiO2 photoelectrode, the different solvent baths have a crucial effect on the dye-sensitized TiO2 photoelectrode. To our knowledge, there is a diversified interaction between the dyes and different solvents [5], which could give a different physical and chemical properties to the dyes adsorbed on the TiO2 surface. Numerous theoretical investigations have examined the adsorption modes of small organic molecules (i.e., formic acid [6–10] and benzoic acid [11,12], isonicotinic acid [13] and bipyridine ligand [14]), small phosphonate group [15], metal-free organic dyes [16–20], and ruthenium-complex [21–25] dyes on TiO2 surface. The overall view extracted from these works indicates an important role of the dye geometry and adsorption energy on the electrochemical properties and efficiencies of DSSCs. Besides, many theoretical studies have also focused on the characterization of the solvent–TiO2 interactions (water [6,26–29] and acetonitrile [6,29,30] in both free and dye-sensitized TiO2). However, a systematic study of the solvent–dye–TiO2 heterointerface, comparing different solvents, and of the associated structural and electronic distribution changes is still very little. In this work, a simple organic dye CD-7 (Fig. 1) was designed and synthesized, and it dissolved in DMF or THF were employed to sensitize TiO2 photoelectrode, and then the photovoltaic and electrochemical impedance performances of the corresponding DSSCs were measured. To gain insight into the effects of different solvent baths on the performances of the corresponding DSSCs, periodic density functional theory (DFT) calculation was used to study the effects of different solvent on the geometry and electronic structure of CD-7 adsorbed on the TiO2 surface.

109

2. Experimental section

110

2.1. Fabrication of DSSCs

111

TiO2 colloid was prepared according to the literature [31]. The washed FTO glass substrates were immersed in

73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107

112

40 mM TiCl4 aq. at 70 °C for 30 min to form a compact layer of TiO2, which plays an important role in suppressing the charge recombination of DSSCs at the interface between FTO and electrolyte, then washed with water and ethanol. A thin film of TiO2 was prepared on the FTO substrate with the compact TiO2 layer through blade coating with glass rod. After drying the nanocrystalline TiO2 layer at 80 °C, the TiO2 thin film with more layers was achieved by repeating the blade coating above process two times. The resulting working electrode was composed of a 14 lm thick transparent TiO2 nanoparticle layer. Finally TiO2 electrodes were treated at 450 °C for 30 min. After cooling to room temperature, the electrodes were immersed in 40 mM TiCl4 aq. at 70 °C for 30 min, and washed with water and ethanol again, then recalcined at 450 °C for 30 min. After the sintering, when the TiO2 electrodes cooled to 80 °C, the electrodes were immersed in the DMF or THF containing 0.2 mM CD-7 for 12 h, respectively. The films were then rinsed in ethanol to remove excess dye. In our experiment, open cells were fabricated in air by clamping the different dye-sensitized electrode with platinized counter electrode. The electrolyte used here is composed of 0.6 M 1,2-dimethyl-3-propylimidazolium iodide (DMPII), 6.53  102 M LiI, 0.03 M I2, 0.28 M 4-ter-

Fig. 2. Geometry-optimized structure of TiO2 anatase (1 0 1) surface.

COOH O O

O O

(a)

H N N

CN O

CD-7

(b)

Scheme 1. Synthetic route of dye CD-7. (a) Ammonium acetate, acetic acid, reflux, 10 h; (b) piperidine, acetonitrile, reflux.

Please cite this article in press as: X. Chen et al., Effects of different solvent baths on the performances of dye-sensitized solar cells: Experimental and theoretical investigation, Org. Electron. (2014), http://dx.doi.org/10.1016/j.orgel.2014.06.026

113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136

ORGELE 2633

No. of Pages 10, Model 3G

4 July 2014 3

35

20000 DMF bath THF bath

15000

DMF bath THF bath

30 25

IPCE (%)

Molar extinction coefficient (M-1 cm-1)

X. Chen et al. / Organic Electronics xxx (2014) xxx–xxx

10000

5000

20 15 10

a

0 300

5 350

400

450

500

0 400

Wavelength (nm)

425

DMF bath THF bath

4.0

0.5

3.5

0.4 0.3 0.2

b

0.0 350

400

450

500

550

600

650

Wavelength (nm) Fig. 3. Absorption spectra of (a) CD-7 in different solvents and (b) the anchored CD-7 on TiO2 surface via different solvents.

138

139 140

tbutylpyridine (TBP) and 0.05 M guanidium thiocyanate (GuSCN) in acetonitrile. 2.2. Fabrication the samples for dye adsorbed amount measurement

146

The measurement of CD-7 adsorbed amount was performed according to the literature [32]. The TiO2 films were prepared same as the fabrication of DSSCs, the 14 lm thickness (area: 8  12 mm) TiO2 films were sensitized for 12 h in DMF or THF bath and employed for the measurement of dye adsorbed amount.

147

2.3. Instruments and measurements

148

Absorption spectra were measured with SHIMADZU (model UV2550) UV–vis spectrophotometer. The irradiation source for the photocurrent action spectrum measurement is a photosource (CHF-XM-500W, Trusttech Co., Ltd., Beijing, China) with a CH Instruments 660C electrochemical workstation (Shanghai CH Instruments Co., China). The incident light intensity was 100 mW cm2 calibrated with a standard Si solar cell. The tested solar cells were masked to a working area of 0.16 cm2. The action spectra of monochromatic incident photon-to-current conversion efficiency (IPCE) for solar cell were performed by using a commercial setup (QTest Station 2000 IPCE Measurement

141 142 143 144 145

149 150 151 152 153 154 155 156 157 158 159

500

525

550

4.5

0.6

Current (mA/cm2 )

Absorbance

0.7

137

475

Wavelength (nm)

0.8

0.1

450

THF bath DMF bath

3.0 2.5 2.0 1.5 1.0 0.5 0.0 0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Voltage (V) Fig. 4. IPCE spectra and J–V curves of DSSCs based on CD-7 sensitized by different solvent.

System, CROWNTECH, USA). Electrochemical impedance spectroscopy (EIS) data were obtained in the dark under forward bias 0.7 V, scanning from 102 to 105 Hz with ac amplitude of 10 mV by using CH Instruments 660C electrochemical workstation.

160

2.4. Synthesis

165

CD-7 was synthesized as shown in Scheme 1. 2.4.1. Synthesis of Compound 1 A acetic acid (20 mL) solution of benzil (313 mg, 1.49 mmol), 1,4-phthalaldehyde (200 mg, 1.49 mmol) and ammonium acetate (1.8 g, 23.8 mmol) were charged sequentially in a three-necked flask and heated under reflux for 10 h. The reaction mixture was poured into icecold water. The resulting precipitate was filtered, washed with water, and dried. Then the residue was purified by silica gel column chromatography with dichloromethane/ ethyl acetate (12:1, v:v) as eluent to afford compound 1 as a yellow solid (225 mg, yield 47%). Mp: 237–239 °C. 1 H NMR d (400 MHz, DMSO-d6): 12.99 (s, 1H), 10.04 (s, 1H), 8.30–8.32 (d, J = 8.4 Hz, 2H), 8.01–8.03 (d, J = 8.4 Hz, 2H), 7.52–7.58 (m, 4H), 7.41–7.49 (m, 3H), 7.25–7.34 (m, 3H). HRMS (ESI, m/z): calcd for C22H16N2O: 324.1263, found 325.1337 [M+H]+.

Please cite this article in press as: X. Chen et al., Effects of different solvent baths on the performances of dye-sensitized solar cells: Experimental and theoretical investigation, Org. Electron. (2014), http://dx.doi.org/10.1016/j.orgel.2014.06.026

161 162 163 164

166

167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182

ORGELE 2633

No. of Pages 10, Model 3G

4 July 2014 4

X. Chen et al. / Organic Electronics xxx (2014) xxx–xxx

Table 1 Photovoltaic performance of DSSCs based on CD-7 sensitized in different solutions. Dye

Solvent

Jsc (mA cm2)

Voc (mV)

FF

se (ms)

g (%)

IPCE (%) (kmax)

CD-7

DMF THF

2.09 3.72

559 588

0.709 0.701

2.77 23.98

0.83 1.53

14 (430 nm) 31 (440 nm)

1.6 1.4 1.2 1.0 0.8

0.4 0.2 DMF

THF

Solvents Fig. 5. Adsorbed amounts of CD-7 on TiO2 film by different solvent.

184 185 186 187 188 189 190 191 192 193 194 195 196 197

214

3. Results and discussion

221

3.1. Photophysical and electrochemical properties

222

Absorption spectra of (a) CD-7 in different solvents and (b) the anchored CD-7 on TiO2 surface via different solvent baths are shown in Fig. 3. In DMF solvent, the UV–vis spectrum of CD-7 exhibit maximal absorption wavelength (kmax) at 366 nm with molar absorption coefficient of 1.40  104 M1 cm1. However, in THF solvent, the UV– vis spectrum of CD-7 exhibit kmax at 374 nm with molar absorption coefficient of 1.20  104 M1 cm1. It is obvious that the kmax of CD-7 in THF is red-shifted in comparison

223

2.4.2. Synthesis of CD-7 A CH3CN (20 mL) solution of compound 1 (80 mg, 0.25 mmol), cyanoacetic acid (63 mg, 0.75 mmol) and a few drops of piperidine were charged sequentially in a three-necked flask and heated under reflux for 6 h. After cooling to room temperature, the solvents were removed by rotary evaporation, and the residue was purified by silica gel column chromatography with dichloromethane/ ethanol (2:1, v:v) as eluent to afford the dye CD-7 as a yellow solid (60 mg, yield 61%). Mp: 258–261 °C. 1H NMR d (400 MHz, DMSO-d6): 13.13 (s, 1H), 8.25–8.27 (d, J = 8.4 Hz, 2H), 8.05 (s, 1H), 7.99–8.0 (d, J = 8.4 Hz, 2H), 7.54–7.56 (d, J = 7.2 Hz, 4H), 7.34–7.37 (m, 6H). HRMS (ESI, m/z): calcd for C25H17N3O2: 391.1321, found 392.1401 [M+H]+.

30

a

DMF bath THF bath

25 20 15 10 5 0 20

30

40

50

60

70

80

90

Z' (ohm) 2.5. Computational methodology

199

In order to study the effects of different solvent baths on the adsorption geometry and electronic structure of CD-7sensitized TiO2, periodic density functional theory (DFT) calculation are performed using a DMol3 package in Materials Studio (version 5.5) [33,34]. All the electronic calculations were made with DN [33] basis sets, and orbital cutoff of 4.5 Å. The exchange–correlation interaction is treated within the generalized gradient approximation (GGA) with the functional parameterized by Perdew, Burke and Ernzerhof (PBE) [35]. To describe core atoms, we used DFT Semi-core Pseudo potentials (DSPPs) [36]. The convergence threshold for the self-consistent field was set to 104 and the smearing was set to 0.005 Hartree in all calculations. The geometry optimization convergence tolerances of the energy, gradient, and displacement are 104 Hartree,

200 202 203 204 205 206 207 208 209 210 211 212 213

-25

b

DMF bath THF bath

-20

Theta (degree)

198

201

215 216 217 218 219 220

0.6

0.0

183

2  103 Hartree Å1, and 5  102 Å, respectively. The crystal model is comprised of (TiO2)48 units, which was extracted from an experimental bulk anatase structure of the MS-software database. The anatase (1 0 1) surface was built by cleaving the horizontal surfaces of TiO2 layers, and creating a vacuum along the c axis. The details of the (TiO2)48 model are shown in Fig. 2.

-Z'' (ohm)

Adsorbed amount (10-4 mM/cm2)

1.8

-15 -10 -5 0 0.1

1

10

100

1000

10000 100000

Frequency (Hz) Fig. 6. EIS spectra of DSSCs based on different solvent bath at 0.70 V forward bias in the dark: (a) Nyquist and (b) Bode phase plots.

Please cite this article in press as: X. Chen et al., Effects of different solvent baths on the performances of dye-sensitized solar cells: Experimental and theoretical investigation, Org. Electron. (2014), http://dx.doi.org/10.1016/j.orgel.2014.06.026

224 225 226 227 228 229 230 231

ORGELE 2633

No. of Pages 10, Model 3G

4 July 2014 X. Chen et al. / Organic Electronics xxx (2014) xxx–xxx

Front of view

Monodentate 1

Monodentate 2

Monodentate 3

Side of view

Monodentate 1

Monodentate 2

Monodentate 3

Fig. 7. Optimized structure of CD-7 adsorbed on (TiO2)48 cluster: Monodentate 1, Monodentate 2, and Monodentate 3.

232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248

with it in DMF, which indicates that there is a different interaction between CD-7 and different solvent molecules (DMF and THF). When it is anchored on 3 lm thick TiO2 film, compared to the spectra in solution, a red-shift and broadening of the absorption spectra were observed, which can be attributed to the formation of J-type aggregation [37]. Compared with CD-7 in DMF or THF, the kmax of CD-7 adsorbed on TiO2 film by DMF or THF bath is redshifted 37 and 30 nm respectively, which indicates that DMF and THF baths have a different effect on the J-aggregation of CD-7. Furthermore, the broadened absorption would be beneficial to the photoelectrical conversion efficiency of the corresponding DSSCs [38]. Besides, the UV– vis spectrum of CD-7-sensitized TiO2 film by THF bath shows a stronger absorption strength than that of DMF bath, which indicates that THF bath is more advantage for CD-7 adsorbing on TiO2 film than that of DMF bath.

5

From the above analysis shown, there is a different interactions between CD-7 and different solvent molecules (DMF and THF), which could give a different effect on the photophysical and chemical properties of the free CD-7 and adsorbed CD-7 on TiO2 surface. With the purpose of studying the effects of solvent baths on the performances of DSSCs, CD-7 in DMF or THF was employed to sensitize TiO2, and then the photovoltaic and electrochemical impedance properties of CD-7-sensitized DSSCs were measured. The IPCE spectra and J–V curves of the corresponding DSSCs are shown in Fig. 4, and corresponding photovoltaic data were collected in Table 1. It is obvious that solvent baths give a big difference in the performances of DSSCs. The DSSC based on THF bath obtained the g value 1.53%, which is about twice as much as that of DMF (g = 0.83%). The Jsc values of DSSCs based on DMF or THF bath are 2.09 and 3.72 mA cm2, respectively, which could be explained by the different IPCE value. The DSSC based THF bath has a broad feature in the action spectrum (400–465 nm) with IPCE value more than 25%, while the corresponding DSSC of DMF bath showed the highest IPCE value as only 14% at 430 nm. To further investigate why the solvent baths could cause such a different performance on DSSCs, the adsorbed amount of CD-7 on TiO2 film based on DMF or THF bath were measured. The adsorbed amounts of CD-7 on TiO2 film are shown in Fig. 5. By desorbing CD-7 into a basic solution, the absorbed amount of CD-7 was estimated by measuring the absorption spectrum of the resultant solution. The coverage density of CD-7-sensitized TiO2 film based on DMF or THF bath were determined to be 1.39  107 and 1.76  107 M cm2, respectively, which could be the main reason why the DSSCs based on THF bath has higher Jsc value than that of DMF bath. Because the increase of dye adsorbed amount could lead to action spectrum broadening and IPCE value increasing [39]. In order to study important interfacial charge transfer processes in DSSCs sensitized by different solvent bath. Electrochemical impedance spectroscopy (EIS) of the DSSCs based on DMF or THF bath were performed to further elucidate the photovoltaic properties. Fig. 6 shows the Nyquist and Bode plots for CD-7-sensitized DSSCs based on DMF or THF bath. For the frequency range investigated (0.1 Hz–100 kHz), a larger semicircle occurs in the lower-frequency range (0.1 Hz to 100 Hz) and a smaller semicircle occurs in the higher-frequency range. With the bias voltage applied, the larger semicircle at lower frequencies corresponded to the charge transfer processes at the TiO2/dye/electrolyte interface, while the smaller semicircle at higher frequencies corresponded to the charge transfer processes at the Pt/electrolyte interface. The difference between the cells in the larger semicircles at lower frequencies was significant. The radius of the lower-frequency semicircle in the Nyquist plot decreased in the following order: THF bath > DMF bath, indicating that the electron recombination resistance in the order as THF bath > DMF bath. To some extent, it is well consistent with the order of decreasing Voc: THF bath (588 mV) > DMF bath (559 mV). The higher Voc of the DSSC based on THF bath can be further explained by electron lifetime (DMF bath is 2.77 ms and THF bath is 23.98 ms), calculated through

Please cite this article in press as: X. Chen et al., Effects of different solvent baths on the performances of dye-sensitized solar cells: Experimental and theoretical investigation, Org. Electron. (2014), http://dx.doi.org/10.1016/j.orgel.2014.06.026

249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309

ORGELE 2633

No. of Pages 10, Model 3G

4 July 2014 6

X. Chen et al. / Organic Electronics xxx (2014) xxx–xxx

Table 2 Main optimized geometrical parameters of the investigated systems on TiO2. Adsorption modes

Bonds

Distance (Å)

Monodentate 1

Ti–O1 O1–C1 O2–C1 O2–H O4–H

2.039 1.298 1.316 1.162 1.301

Ti–O1 O1–C1 O2–C1 O2–H O3–H

2.106 1.304 1.314 1.161 1.280

Ti–O1 O1–C1 O2–C1 O2–H O3–H

1.934 1.346 1.273 1.797 1.020

Ti2–O2 Ti1–O1 O1–C1 O2–C1 O3–H

2.032 2.097 1.300 1.323 0.981

Ti2–O2 Ti1–O1 O1–C1 O2–C1 O3–H

2.075 2.093 1.296 1.319 0.982

Ti2–O2 Ti1–O1 O1–C1 O2–C1 O3–H

2.074 2.092 1.299 1.317 0.982

Monodentate 2

Monodentate 3

Bidentate 4

Bidentate 4 coadsorbed with DMF

Bidentate 4 coadsorbed with THF

310 311 312 313 314

the relation se ¼ 21pf (f is the peak frequency of lower-frequency range in EIS Bode plot) [40]. From the above analysis, it could be concluded that different solvent baths could give a big effect on the electron lifetime of the corresponding DSSCs.

315

3.2. Results and discussion of theoretical calculations

316

3.2.1. Monodentate adsorption mode So far, lots of efforts have been given into the process of studying dyes–TiO2 adsorption, in which the adsorption of the dyes through carboxylic acid can be either physisorption (via hydrogen bonding between oxygen atom on TiO2 surface and hydrogen atom of the dye) or chemisorption (H atom of carboxylic acid dissociates, and the bond is formed between carboxylic oxygen atoms and the surface titanium atoms of TiO2, which can be of monodentate ester, bidentate chelating, or bidentate bridging types) [8,41]. In this paper, we have identified four different adsorption mode of CD-7 on the TiO2 surface. Starting from the geometries optimized in vacuum, we added the solvent molecules, DMF or THF, so as to saturate the possible absorption site of fivefold coordinated Ti sites on the TiO2 surface. The optimized monodentate adsorption modes of CD-7 on (TiO2)48 cluster are shown in Fig. 7, and the main optimized geometrical parameters are listed in Table 2. As

317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334

shown in Table 2, the O1–C1 and O2–C1 bond lengths in Monodentate 1 and 2 are symmetrical: the O1–C1 distances are 1.298 Å and 1.304 Å, whereas O2–C1 is 1.316 Å and 1.314 Å, respectively. However, it is worth noting that the O1–C1 and O2–C1 bond lengths became asymmetrical in the Monodentate 3. The O2–C1 distance is 1.273 Å, indicating a carbonyl bond, whereas O1–C1 distance is 1.346 Å, indicating a hydroxylic bond. From the view of the monodentate adsorption modes, the main difference in the Monodentate 3 is that the proton H transfer from carboxylic acid group to the O3 site and the deprotonated carboxylic moiety form the carbonyl bond, which could be the main reason that causes the asymmetrical between O1– C1 and O2–C1. The O2–H bond lengths is about 1.160 Å in Monodentate 1 and 2, while the O3–H bond lengths is 1.020 Å in the Monodentate 3, indicating that the deprotonation is advantage to stabilizing the chemical bond between the hydrogen and oxygen atom.

335

3.2.2. Bidentate adsorption mode As shown in Fig. 8, in Bidentate 4, both carboxylic oxygen atoms (O1 and O2) are bonded to two fivefold coordinated Ti atoms, whereas the acid hydrogen atom (H) is bonded to the bridging oxygen O3 on the TiO2 surface. As shown in Table 2, Ti1–O1 and Ti2–O2 in vacuum are asymmetric, whose bond distances are 2.097 and 2.032 Å, respectively. When CD-7 is coadsorbed with DMF or THF molecules, the symmetry was increased between the Ti1–O1 and Ti2–O2, showing difference of only 0.018 Å. The C1–O1 and C1–O2 bond distances show difference as 0.023 Å in vacuum or in presentation of DMF, whereas the difference is 0.018 Å in presentation of THF, which indicates that the coadsorbed THF is advantage to increase the symmetry between the C1–O1 and C1–O2. However, the O3–H bond distance always keeps about 0.982 Å whether the geometry in vacuum or in presentation of DMF or THF, which indicates that the coadsorbed solvent molecules could not change the stability of the proton H absorbed on the TiO2 surface.

353

3.2.3. Adsorption energies After optimization, the adsorption energies (Eads) of the solvent molecules and dyes on (TiO2)48 cluster were obtained by using the equation given below:

373

Eads ðkcal=molÞ ¼ EDye=Solvent þ ETiO2  EDye=SolventTiO2 ½42 where EDye/Solvent is the total energy of isolated dye or solvent molecule, ETiO2 is the total energy of (TiO2)48 cluster, and EDye/Solvent–TiO2 is the total energy of dye–TiO2 or solvent–TiO2 complex. Following the above expression, positive values of Eads correspond to a stable adsorption on the surface. The computed Eads for the four absorption modes of CD-7 are reported in Table 3 as 60.08, 48.43, 58.23 and 62.65 kcal/mol, respectively. From the view of the absorption energies, the most stable adsorption mode is the Bidentate 4, expressing that the main adsorption mode is the bidentate adsorption mode, which is good in agreement with many experiments results [41,43,44]. So, only this adsorption mode is presented in our study to investigate the effects of DMF and THF baths on the asso-

Please cite this article in press as: X. Chen et al., Effects of different solvent baths on the performances of dye-sensitized solar cells: Experimental and theoretical investigation, Org. Electron. (2014), http://dx.doi.org/10.1016/j.orgel.2014.06.026

336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352

354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372

374 375 376

377 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393

ORGELE 2633

No. of Pages 10, Model 3G

4 July 2014 X. Chen et al. / Organic Electronics xxx (2014) xxx–xxx

Front of view

Side of view

Bidentate 4 in vacuum

Bidentate 4 in vacuum

Bidentate 4 coadsorbed with DMF

Bidentate 4 coadsorbed with DMF

Bidentate 4 coadsorbed with THF

Bidentate 4 coadsorbed with THF

7

Fig. 8. Optimized structure of CD-7 adsorbed on TiO2 (1 0 1) surface: Bidentate 4, Bidentate 4 coadsorbed with DMF, Bidentate 4 coadsorbed with THF.

Table 3 Adsorption energy of CD-7 or solvent molecules adsorbed on TiO2 (1 0 1) surface in vacuum.

394 395

Adsorption modes

Eads (kcal/mol)

Monodentate 1 Monodentate 2 Monodentate 3 Bidentate 4 DMF–TiO2 THF–TiO2

60.08 48.43 58.23 62.65 38.34 36.74

ciated structural and electronic distribution of CD-7 on the TiO2 surface.

3.2.4. Adsorption of solvent molecules To gain insight into the effects of adsorbed DMF and THF on the TiO2 (1 0 1) surface, we also studied the TiO2 (1 0 1) adsorbed with solvent molecules. The optimized geometry structures are shown in Fig. 9, both DMF and THF adsorbed on the TiO2 (1 0 1) surface through the fivefold coordinated Ti sites with Ti–O bond distances as 2.047 and 2.197 Å, respectively. It is worth noting that they have different adsorption angles on the TiO2 surface (DMF is 93.75° and THF is 84.23°), which indicates that DMF molecule has a bigger steric hindrance on the TiO2 (1 0 1) surface. Besides, according to the Eads of the solvent molecules (Table 3), we can approximate the relative affinity of DMF

Please cite this article in press as: X. Chen et al., Effects of different solvent baths on the performances of dye-sensitized solar cells: Experimental and theoretical investigation, Org. Electron. (2014), http://dx.doi.org/10.1016/j.orgel.2014.06.026

396 397 398 399 400 401 402 403 404 405 406 407 408

ORGELE 2633

No. of Pages 10, Model 3G

4 July 2014 8

X. Chen et al. / Organic Electronics xxx (2014) xxx–xxx

HOMO

LUMO

Top view

CD-7-TiO2

Side view

THF-TiO 2

DMF-TiO 2

DMF-CD-7-TiO2

Fig. 9. Optimized structure of solvent molecule DMF and THF adsorbed on TiO2 (1 0 1) surface.

410 411 412 413 414 415 416 417 418 419 420 421 422

423 424 425 426 427 428 429 430 431

and THF for anchoring to the bare TiO2 surface. The Eads of DMF-TiO2 and THF-TiO2 are 38.34 and 36.74 kcal/mol, respectively, expressing that DMF molecule is easier adsorbed on the TiO2 surface than THF molecule. The two factors could give a direct effect on the adsorption amount, so the adsorption amount of CD-7 on the TiO2 film based on THF bath is more than that of DMF bath, which is in excellent agreement with the adsorbed amount measurement (Fig. 5). The density of states (DOSs) for a bare TiO2, DMF-TiO2 and THF-TiO2 are presented in Fig. 10. Compared with the DOSs of bare TiO2, A, B, C, D and E peaks appears in the bandgap of TiO2 when TiO2 surface is adsorbed with DMF or THF, which would decrease the bandgap of TiO2 and be conducive to the electron transmission.

THF-CD-7-TiO2

Fig. 11. The electron distributions of HOMOs and LUMOs for CD-7-TiO2, DMF-CD-7-TiO2 and THF-CD-7-TiO2 adsorbed on TiO2 (1 0 1) surface.

3.2.5. Electronic structure of dye-sensitized TiO2 with the presence of the solvent molecules The electron distributions of HOMOs and LUMOs for CD-7-TiO2, DMF-CD-7-TiO2 and THF-CD-7-TiO2 have been described in Fig. 11. As shown in Fig. 11, the electron distribution in the HOMOs mostly delocalize on CD-7, whereas the LUMOs show injected electron delocalized dominantly on TiO2 surface. These results indicated that intermolecular charge transfer (CT) transition take place

Density of States (electrons/Ha)

409

in the CD-7-TiO2 cluster through the carboxylic acid anchoring on TiO2 surface. When CD-7 is coadsorbed with DMF or THF, there is no change in the electron distributions of the HOMO and LUMO, which indicated that the adsorbed solvent molecules have little effect on the electron distributions the CD-7-TiO2 cluster. As shown in Fig. 12, the DOS of CD-7-TiO2 complexes is similar to that of (TiO2)48 cluster showing two strong bands, CB and

5000 4000

TiO 2 DMF-TiO2

3000

THF-TiO 2

2000 1000 A

0 -0.8

-0.7

-0.6

-0.5

B

C

-0.4

D E

-0.3

-0.2

-0.1

0.0

0.1

0.2

Energy (Ha) Fig. 10. DOS of bare TiO2, DMF-TiO2 and THF-TiO2.

Please cite this article in press as: X. Chen et al., Effects of different solvent baths on the performances of dye-sensitized solar cells: Experimental and theoretical investigation, Org. Electron. (2014), http://dx.doi.org/10.1016/j.orgel.2014.06.026

432 433 434 435 436 437 438 439

ORGELE 2633

No. of Pages 10, Model 3G

4 July 2014 9

X. Chen et al. / Organic Electronics xxx (2014) xxx–xxx

4000

TiO 2 CD7 CD7-TiO2

3000

DMF-CD7-TiO2

2000

THF-CD7-TiO 2

5000

Density of States(electrons/Ha)

1000 0 5000

LUMO Electronic coupling

4000 3000 2000 1000 0 5000

LUMO

4000 3000 2000 1000 0 5000

LUMO

4000 3000 2000 1000 0 -0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

Energy(Ha) Fig. 12. DOS of bare TiO2, CD-7, CD-7-TiO2, DMF-CD-7-TiO2 and THF-CD-7-TiO2. 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456

valence band edges of TiO2. However, it is obvious that the peak intensities of CD-7-TiO2 complexes in CB edge were higher and sharper than those of bare TiO2 substrate, indicating a strong electronic coupling between the LUMO of dye and the CB of TiO2. Besides, there are appearances of new peaks in the bandgap of TiO2 in the DOS of CD-7TiO2 complexes in comparison with that of bare TiO2, which would decrease the bandgap of TiO2 and be conducive to the electron transmission. Compared with the energy level of CD-7-TiO2 in the LUMO orbital, the energy level of both DMF-CD-7-TiO2 and THF-CD-7-TiO2 have an increase as 0.020 and 0.016 Ha, respectively. However, the EIS spectra indicates that the injected electron in DMF-CD-7-TiO2 is easier to recombine with the I/I3 than that of THF-CD-7-TiO2. The electron lifetimes of DSSCs may be the main factor affecting the Voc, so that the DSSC based on THF bath has an bigger Voc than that of DMF bath.

457

4. Conclusion

458

In this paper, with the purpose of understanding the effects of different solvent baths on the performances of DSSCs, the analysis methods of experiment and computational modeling are used to investigate CD-7-sensitized DSSCs via THF or DMF bath. In experiment, the photophysical of CD-7 in THF or DMF, and the performances of DSSCs based on THF or DMF bath are investigated. Absorption spectrum of CD-7 in THF is red-shifted in comparison with it in DMF, indicating that there is a different interaction between CD-7 and THF or DMF molecule. Besides, the

459 460 461 462 463 464 465 466 467

spectra of CD-7 adsorbed on TiO2 film show that different solvent bath gives a different effect on the J-aggregation and absorption strength. IPCE spectra and electrochemistry analyses show that the different solvent baths will give a significant effect on the IPCE value and electron lifetime of the corresponding DSSCs. The CD-7-sensitized DSSC via THF bath obtained the g value 1.53%, which is about twice as much as that of DMF bath. The results of computational modeling are in good agreement with the experiment analyses. The adsorbed DMF and THF will affect the energy level of TiO2, adsorption structure and adsorbed amount of CD-7 on the TiO2 film. The different steric hindrance and adsorption energies between THF and DMF molecule on TiO2 (1 0 1) surface could be the essential reason why CD-7 sensitized TiO2 film based on THF bath has a larger adsorption amount than that of DMF bath. Therefore, this study gets new insights into the understanding of the solvent effects on the performances of DSSCs and may assist the improvement in the preparation of the dye-sensitized TiO2 photoelectrode.

468

Acknowledgments

488

We thank the National Natural Science Foundation of Q2 China (Grant No. 21272033), the Innovation Funds of State Q3 key Laboratory of Electronic Thin Films and Integrated Device (Grant No. CXJJ201104), National Science and Technology Major Project of the Ministry of Environmental Protection of China (2012ZX07203-003-Z04) and Key Laboratory of Functional Inorganic Material Chemistry

489

Please cite this article in press as: X. Chen et al., Effects of different solvent baths on the performances of dye-sensitized solar cells: Experimental and theoretical investigation, Org. Electron. (2014), http://dx.doi.org/10.1016/j.orgel.2014.06.026

469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487

490 491 492 493 494 495

ORGELE 2633

No. of Pages 10, Model 3G

4 July 2014 10

X. Chen et al. / Organic Electronics xxx (2014) xxx–xxx

497

(Heilongjiang University), Ministry of Education of China for financial support.

498

References

499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571

[1] B. O’Regan, M. Gratzel, A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films, Nature 353 (1991) 737–740. [2] M. Grätzel, Recent advances in sensitized mesoscopic solar cells, Acc. Chem. Res. 42 (2009) 1788–1798. [3] L. Han, A. Islam, H. Chen, C. Malapaka, B. Chiranjeevi, S. Zhang, X. Yang, M. Yanagida, High-efficiency dye-sensitized solar cell with a novel co-adsorbent, Energy Environ. Sci. 5 (2012) 6057–6060. [4] S. Mathew, A. Yella, P. Gao, R. Humphry-Baker, F.E. CurchodBasile, N. Ashari-Astani, I. Tavernelli, U. Rothlisberger, K. NazeeruddinMd, M. Grätzel, Dye-sensitized solar cells with 13% efficiency achieved through the molecular engineering of porphyrin sensitizers, Nat. Chem. 6 (2014) 242–247. [5] R. Chen, G. Zhao, X. Yang, X. Jiang, J. Liu, H. Tian, Y. Gao, X. Liu, K. Han, M. Sun, L. Sun, Photoinduced intramolecular charge-transfer state in thiophene-p-conjugated donor-acceptor molecules, J. Mol. Struct. 876 (2008) 102–109. [6] W.-K. Li, X.-Q. Gong, G. Lu, A. Selloni, Different reactivities of TiO2 polymorphs: comparative DFT calculations of water and formic acid adsorption at anatase and brookite TiO2 surfaces, J. Phys. Chem. C 112 (2008) 6594–6596. [7] X.-Q. Gong, A. Selloni, A. Vittadini, Density functional theory study of formic acid adsorption on anatase TiO2 (0 0 1): geometries, energetics, and effects of coverage, hydration, and reconstruction, J. Phys. Chem. B 110 (2006) 2804–2811. [8] A. Vittadini, A. Selloni, F.P. Rotzinger, M. Gratzel, Formic acid adsorption on dry and hydrated TiO2 anatase (1 0 1) surfaces by DFT calculations, J. Phys. Chem. B 104 (2000) 1300–1306. [9] K.L. Miller, C.B. Musgrave, J.L. Falconer, J.W. Medlin, Effects of water and formic acid adsorption on the electronic structure of anatase TiO2 (1 0 1), J. Phys. Chem. C 115 (2011) 2738–2749. [10] K.L. Miller, J.L. Falconer, J.W. Medlin, Effect of water on the adsorbed structure of formic acid on TiO2 anatase (1 0 1), J. Catal. 278 (2011) 321–328. [11] N. Martsinovich, D.R. Jones, A. Troisi, Electronic structure of TiO2 surfaces and effect of molecular adsorbates using different DFT implementations, J. Phys. Chem. C 114 (2010) 22659–22670. [12] N. Martsinovich, A. Troisi, Theoretical studies of dye-sensitised solar cells: from electronic structure to elementary processes, Energy Environ. Sci. 4 (2011) 4473–4495. [13] M. Nilsing, P. Persson, L. Ojamae, Anchor group influence on molecule–metal oxide interfaces: periodic hybrid DFT study of pyridine bound to TiO2 via carboxylic and phosphonic acid, Chem. Phys. Lett. 415 (2005) 375–380. [14] P. Hirva, M. Haukka, Effect of different anchoring groups on the adsorption of photoactive compounds on the anatase (1 0 1) surface, Langmuir 26 (2010) 17075–17081. [15] V.M. Bermudez, Computational study of the adsorption of dimethyl methylphosphonate (DMMP) on the (0 1 0) surface of anatase TiO2 with and without faceting, Surf. Sci. 604 (2010) 706–712. [16] N. Martsinovich, A. Troisi, High-throughput computational screening of chromophores for dye-sensitized solar cells, J. Phys. Chem. C 115 (2011) 11781–11792. [17] K. Srinivas, G. Sivakumar, C. Ramesh Kumar, M. Ananth Reddy, K. Bhanuprakash, V.J. Rao, C.-W. Chen, Y.-C. Hsu, J.T. Lin, Novel 1,3,4oxadiazole derivatives as efficient sensitizers for dye-sensitized solar cells: a combined experimental and computational study, Synth. Met. 161 (2011) 1671–1681. [18] M. Pastore, F.D. Angelis, Aggregation of organic dyes on TiO2 in dyesensitized solar cells models: an ab initio investigation, ACS Nano 4 (2009) 556–562. [19] D. Rocca, R. Gebauer, F. De Angelis, M.K. Nazeeruddin, S. Baroni, Time-dependent density functional theory study of squaraine dyesensitized solar cells, Chem. Phys. Lett. 475 (2009) 49–53. [20] P. Chen, J.H. Yum, F.D. Angelis, E. Mosconi, S. Fantacci, S.-J. Moon, R.H. Baker, J. Ko, M.K. Nazeeruddin, M. Gratzel, High open-circuit voltage solid-state dye-sensitized solar cells with organic dye, Nano Lett. 9 (2009) 2487–2492. [21] F. De Angelis, S. Fantacci, A. Selloni, M. Gratzel, M.K. Nazeeruddin, Influence of the sensitizer adsorption mode on the open-circuit potential of dye-sensitized solar cells, Nano Lett. 7 (2007) 3189– 3195. [22] F. De Angelis, S. Fantacci, A. Selloni, M.K. Nazeeruddin, M. Gratzel, First-principles modeling of the adsorption geometry and electronic

496

[23]

[24]

[25]

[26] [27]

[28] [29]

[30]

[31]

[32]

[33]

[34] [35] [36] [37]

[38]

[39]

[40]

[41]

[42]

[43]

[44]

structure of Ru(II) dyes on extended TiO2 substrates for dyesensitized solar cell applications, J. Phys. Chem. C 114 (2010) 6054–6061. F. De Angelis, S. Fantacci, A. Selloni, M.K. Nazeeruddin, M. Gratzel, Time-dependent density functional theory investigations on the excited states of Ru(II)-dye-sensitized TiO2 nanoparticles: the role of sensitizer protonation, J. Am. Chem. Soc. 129 (2007) 14156–14157. F. De Angelis, S. Fantacci, E. Mosconi, M.K. Nazeeruddin, M. Gratzel, Absorption spectra and excited state energy levels of the N719 dye on TiO2 in dye-sensitized solar cell models, J. Phys. Chem. C 115 (2011) 8825–8831. F. Labat, I. Ciofini, H.P. Hratchian, M.J. Frisch, K. Raghavachari, C. Adamo, Insights into working principles of ruthenium polypyridyl dye-sensitized solar cells from first principles modeling, J. Phys. Chem. C 115 (2011) 4297–4306. A. Tilocca, A. Selloni, Vertical and lateral order in adsorbed water layers on anatase TiO2 (1 0 1), Langmuir 20 (2004) 8379–8384. H. Cheng, A. Selloni, Hydroxide ions at the water/anatase TiO2 (1 0 1) interface: structure and electronic states from first principles molecular dynamics, Langmuir 26 (2010) 11518–11525. J. Cheng, M. Sprik, Aligning electronic energy levels at the TiO2/H2O interface, Phys. Rev. B 82 (2010) 081406. E. Mosconi, A. Selloni, F. De Angelis, Solvent effects on the adsorption geometry and electronic structure of dye-sensitized TiO2: a firstprinciples investigation, J. Phys. Chem. C 116 (2012) 5932–5940. F. Schiffmann, J. VandeVondele, J. Hutter, R. Wirz, A. Urakawa, A. Baiker, Protonation-dependent binding of ruthenium bipyridyl complexes to the anatase (1 0 1) surface, J. Phys. Chem. C 114 (2010) 8398–8404. J. Liu, H. Yang, W. Tan, X. Zhou, Y. Lin, Photovoltaic performance improvement of dye-sensitized solar cells based on tantalum-doped TiO2 thin films, Electrochim. Acta 56 (2010) 396–400. H.N. Tian, X.C. Yang, R.K. Chen, R. Zhang, A. Hagfeldt, L.C. Sunt, Effect of different dye baths and dye-structures on the performance of dyesensitized solar cells based on triphenylamine dyes, J. Phys. Chem. C 112 (2008) 11023–11033. B. Delley, An all-electron numerical method for solving the local density functional for polyatomic molecules, J. Chem. Phys. 92 (1990) 508–517. B. Delley, From molecules to solids with the DMol3 approach, J. Chem. Phys. 113 (2000) 7756–7764. J.P. Perdew, K. Burke, M. Ernzerhof, Generalized gradient approximation made simple, Phys. Rev. Lett. 77 (1996) 3865–3868. B. Delley, Hardness conserving semilocal pseudopotentials, Phys. Rev. B 66 (2002) 155125. Z.-S. Wang, K. Hara, Y. Dan-oh, C. Kasada, A. Shinpo, S. Suga, H. Arakawa, H. Sugihara, Photophysical and (photo)electrochemical properties of a coumarin dye, J. Phys. Chem. B 109 (2005) 3907– 3914. M. Guo, P. Diao, Y.-J. Ren, F. Meng, H. Tian, S.-M. Cai, Photoelectrochemical studies of nanocrystalline TiO2 co-sensitized by novel cyanine dyes, Sol. Energy Mater. Sol. C 88 (2005) 23–35. E.L. Tae, S.H. Lee, J.K. Lee, S.S. Yoo, E.J. Kang, K.B. Yoon, A strategy to increase the efficiency of the dye-sensitized TiO2 solar cells operated by photoexcitation of dye-to-TiO2 charge-transfer bands, J. Phys. Chem. B 109 (2005) 22513–22522. W. Li, Y. Wu, Q. Zhang, H. Tian, W. Zhu, D-A-p-A featured sensitizers bearing phthalimide and benzotriazole as auxiliary acceptor: effect on absorption and charge recombination dynamics in dye-sensitized solar cells, ACS Appl. Mater. Inter. 4 (2012) 1822–1830. M.K. Nazeeruddin, R. Humphry-Baker, P. Liska, M. Gratzel, Investigation of sensitizer adsorption and the influence of protons on current and voltage of a dye-sensitized nanocrystalline TiO2 solar cell, J. Phys. Chem. B 107 (2003) 8981–8987. S. Jungsuttiwong, T. Yakhanthip, Y. Surakhot, J. Khunchalee, T. Sudyoadsuk, V. Promarak, N. Kungwan, S. Namuangruk, The effect of conjugated spacer on novel carbazole derivatives for dye-sensitized solar cells: density functional theory/time-dependent density functional theory study, J. Comput. Chem. 33 (2012) 1517–1523. T. Yakhanthip, S. Jungsuttiwong, S. Namuangruk, N. Kungwan, V. Promarak, T. Sudyoadsuk, P. Kochpradist, Theoretical investigation of novel carbazole–fluorene based D-p-A conjugated organic dyes as dye-sensitizer in dye-sensitized solar cells (DSCs), J. Comput. Chem. 32 (2011) 1568–1576. K. Hara, T. Sato, R. Katoh, A. Furube, Y. Ohga, A. Shinpo, S. Suga, K. Sayama, H. Sugihara, H. Arakawa, Molecular design of coumarin dyes for efficient dye-sensitized solar cells, J. Phys. Chem. B 107 (2002) 597–606.

Please cite this article in press as: X. Chen et al., Effects of different solvent baths on the performances of dye-sensitized solar cells: Experimental and theoretical investigation, Org. Electron. (2014), http://dx.doi.org/10.1016/j.orgel.2014.06.026

572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650